Abstract

Imagine that you are a detective investigating a murder. You have a body that was found in a swimming pool, and someone reported hearing an argument near the pool at 10:00 PM the night before. Your first question might be "Was this person killed around 10:00 PM last night, or at some other time?" One way to answer this question is to measure the internal temperature of the body. The longer ago the killing occurred, the colder the body. But can you assign a specific time of death to a specific temperature? In this science fair project, you will measure the rate of heat loss from an orange and see how it depends on the temperature of the surroundings.

Objective

Measure the rate of heat loss from an orange (representing a body) and see how it depends on the temperature of the surroundings.

APA Style

Science Buddies Staff.
(2014, October 23).
Investigate the 'Death' of an Orange: How is Rate of Heat Loss Based on the Surrounding Temperature?.
Retrieved March 3, 2015
from http://www.sciencebuddies.org/science-fair-projects/project_ideas/Phys_p079.shtml

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Introduction

Say you are investigating a murder and want to know when the victim was killed. If the body is cold, you can guess that the murder did not happen very recently. But can you be more precise in order to catch the killer? First, you will want to measure the internal temperature of the body, its core temperature. Once you have the core temperature, what else do you need to know to determine when the murder took place? Well, you will want to know what the temperature of the surroundings was in the recent past. If the body was found in the morning, you will want to know what the temperature in the area was overnight, for example. You will also want to determine if the body was insulated, say, by heavy clothing. More clothing will obviously slow the rate of heat loss. Suppose the body was found in a swimming pool or in a lake. How would this affect the rate of heat loss? These are all questions that you can model, without having to work with actual victims. In this case, you will use an orange as a model for a human body. One concept that is particularly important for this science fair project is rate of change. See Equation 1.

Equation 1:

Rate of change = Change in temperature (°C)/time (hours)

If the temperature of an object decreases by 10°Celsius (C) in 1 hour (h), the rate of change of the temperature is -10°C/h—the negative sign indicates that the temperature is going down. If the temperature of an object decreases by 10°C in 10 h, the rate of change is -1°C/h (10 divided by 10 is 1, and the answer is -1 because again, the temperature is going down). The change in temperature is the same (10°C) in both cases, but one rate is 10 times greater than the other. The time can be calculated in seconds, minutes, days, or in any other time unit.

In this forensics science fair project, you will investigate the "time of death" of an orange. The orange will be warmed to near human core body temperature (100°F) and allowed to cool for various amounts of time in surroundings of various temperatures. You will make a graph that shows how the temperature changes over time. You can also investigate how factors such as clothing and size affect heat loss.

Terms and Concepts

Core temperature

Heat loss

Model

Rate of change

Forensics

Questions

What is the "normal" core temperature of the human body?

How would the size of an object affect the rate of change in temperature?

How would the shape of an object affect the rate of change in temperature? (Interesting fact: A sphere has the smallest surface area possible for a given volume, so it will theoretically have the slowest rate of change.)

How would other factors affect rate of heat loss? For example, consider humidity levels, air movement, and fat levels in the body.

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Materials and Equipment

Cooler, StyrofoamTM

Thermometer, with stainless steel stem to insert into the orange. Obtain 2 thermometers if you want to measure temperature in two oranges at the same time. Use a thermometer that is meant for measuring ambient temperatures (meaning, temperatures around the house or outside). Thermometers for body temperature or for oven use may be suitable. Should have clear readings between 50 and 100°F (10–38°C ). For example, this pocket thermometer from www.amazon.com

Tap water

Lab notebook

Pot, 1-gallon

Oranges (6), should be the same size

Stove

Tongs

Timer

Ice (1 bag)

Graph paper

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Variations

Try larger or smaller oranges. How does the rate of change in the temperature vary with the diameter of the orange?

Determine the rate of cooling (in air, not in water) when the orange is placed on a piece of Styrofoam vs. sitting on a metal surface.

"Dress" the orange; for example, with duct tape. How does this affect heat loss?

Cool the oranges at other temperatures, such as 40°F, 50°F, and 60°F. Add ice or cold water to keep the temperature of the water bath constant. How does the rate of change of the temperature vary with the temperature difference?

Ask an Expert

The Ask an Expert Forum is intended to be a place where students can go to find answers to science questions that they have been unable to find using other resources. If you have specific questions about your science fair project or science fair, our team of volunteer scientists can help. Our Experts won't do the work for you, but they will make suggestions, offer guidance, and help you troubleshoot.

Related Links

If you like this project, you might enjoy exploring these related careers:

Forensic Science Technician

Guilty or not guilty? The fate of the accused in court lies with the evidence gathered at the crime scene. The job of the forensic science technician is to gather evidence and use scientific principles and techniques to make sense of it. It can be a grueling and graphic job, but very rewarding. If you like the idea of using science to help deliver justice, then you should investigate this career.
Read more

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